Vehicle supplemental restraint systems perform a number of functions including acceleration sensing, signal processing and analysis, and deployment of one or more restraint devices such as frontal or side air bags and seat belt pretensioners in response to a sensed crash event. Typically, the acceleration signal is monitored to detect the onset of a crash event (as indicated by acceleration in excess of a reference value, for example), and then filtered or integrated over the course of the crash event to determine the change in velocity due to the crash. The change in velocity (ΔV) is indicative of the crash severity, and may be compared to a calibrated threshold to determine if the crash event is sufficiently severe to warrant deployment of restraints. Other measures of crash severity may also be used.
While being conceptually simple, the above-described approach can be problematic in practice because it is sometimes difficult to rule out acceleration disturbances due to rough road surfaces, particularly when the deployment decision must be made in a very early stage of the crash event. It can also be difficult to reliably distinguish between deployment crash events and non-deployment crash events, particularly since non-deployment events sometimes result in relatively high ΔV levels in the later stage of the crash event. Many procedures and rules have been devised for overcoming these problems, but they tend to be overly complicated and heuristic in nature rather than physics-based. Accordingly, what is needed is a physics-based, easily implemented method of providing immunity from deployment due to rough road surfaces and other non-crash events and reliably distinguishing between deployment and non-deployment crash events, while providing timely and reliable deployment determination.